The present invention relates to a method of controlling the ignition timing of an internal combustion engine.
A well-known method of controlling the ignition timing of the engine consists in detecting the flow rate of the intake air or the pneumatic pressure in the intake manifold and the rotational speed as operating condition parameters, calculating an optimum ignition timing from the detected operating condition parameters by using a predetermined function which represents the relationship between optimum ignition timings and the operating condition parameters, and practically adjusting the ignition timing responsive to the calculated value. The optimum ignition timing should be selected to a value that is advanced as much as possible in such a manner that a maximum torque can be obtained without development of knocking under any operating condition.
According to the conventional control method of this type, however, the function has been determined so that optimum ignition timings are obtained when the engine is completely warmed up and when the engine is under ordinary operating conditions. In other words, no countermeasure has been provided to cope with the cases when the temperature of the engine is excessively raised or when the engine is overheated to some extent. Therefore, when overheated, the engine tends to knock. In extreme cases, there develops pre-ignition which may cause the engine to be damaged.